Aquaculture 238 (2004) 195 – 205
www.elsevier.com/locate/aqua-online
Rearing performance of Spongia officinalis on
suspended ropes off the Southern Italian Coast
(Central Mediterranean Sea)
Giuseppe Corriero a,*, Caterina Longo a, Maria Mercurio a,
Carlotta Nonnis Marzano a, Giuseppe Lembo b,
Maria Teresa Spedicatob
a
Dipartimento di Zoologia dell’Università, Universita di Bari, via Orabona 4 - 70125-Bari, Italy
COISPA Tecnologia and Ricerca, Stazione Sperimentale per lo Studio delle Risorse del Mare,
via dei Trulli, 18/20, 70045, Torre a Mare, Bari, Italy
b
Received 17 November 2003; received in revised form 22 April 2004; accepted 26 April 2004
Abstract
The availability of bath sponges has been recently reduced due to the depletion of natural banks
due to the high fishing pressure together with some local epidemic events. At present, the
commercial supply is far below the demand. The main purpose of this work was to estimate the
rearing performance of Spongia officinalis var. adriatica, one of the most common Mediterranean
commercial sponges, testing two different variants of culture on suspended ropes: a horizontal
system placed close to the seabed, and a vertical system extended along the water column. The
trials were carried out in Southern Italy (Ionian coast of Apulia, Central Mediterranean) from April
1997 to April 2000. Wild specimens of sponge were cut into pieces of different weight to test
possible differences in growth and survival. During the study period, both systems resisted
deterioration due to water movement and other ecological factors. In general, the growth
performance (average weight, specific growth rate) did not significantly vary between the
cultivation systems, nor were statistical differences in growth detected between the cuttings of
different initial size. The mean growth observed was rather variable among sponge cuttings, even
considering the same rearing condition and size range. The measured variations of hydrological
parameters did not seem to affect survival, growth performance, or reproductive activity, which was
detected almost all year round. Larger explants (about 50 g in wet weight) reached the commercial
size after three years of rearing, thus identifying this initial size as the most suitable for cultivation
* Corresponding author. Dipartimento di Zoologia dell’Università, Universita di Bari, via Orabona 4 - 70125Bari, Italy. Tel./fax: +39-80-5443357.
E-mail address: g.corriero@biologia.uniba.it (G. Corriero).
0044-8486/$ - see front matter D 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.aquaculture.2004.04.030
196
G. Corriero et al. / Aquaculture 238 (2004) 195–205
purposes. At the end of the study period, the survival rate was 75%, with a more apparent decrease
during the first year of rearing.
D 2004 Elsevier B.V. All rights reserved.
Keywords: Spongia officinalis; Growth rate; Rearing; Survival
1. Introduction
The current world market for bath sponges is dominated by the artificial products,
although the value and the advantages of natural sponges are widely recognised. The
present supply of natural sponges is outstripped by demand and is sustained worldwide by
the wild Caribbean product, which has replaced the more precious Mediterranean sponge
since the 1980s. Indeed, the availability of Mediterranean sponges was dramatically
reduced by the depletion of natural banks, due both to high fishing pressure and devastating
epidemic events (Gaino and Pronzato, 1989, 1992; Gaino et al., 1992, 1994; Vacelet et al.,
1994; Pronzato, 1999). Attempts at bath sponge cultivation have been performed since the
end of the nineteenth century (Osinga et al., 1999; Brümmer and Nickel, 2003), although
only more recently have such investigations identified proper rearing techniques of sponge
culture (Stevely et al., 1978; Verdenal and Verdenal, 1987; Verdenal and Vacelet, 1990;
Grovas, 1998; Scalera Liaci et al., 1999). However, the available data on the rearing
performance especially in terms of growth are not strictly comparable.
Sponge farming, which is an easy low-technology activity (Scalera Liaci et al., 1999),
could play a notable role in the context of Mediterranean aquaculture, where the
diversification of species and rearing systems is considered an important challenge for
the future (Paquotte, 1998). Moreover, at present, the need for good-quality bath sponges
is accompanied worldwide by a high demand for other sponge species which produce
bioactive compounds useful for medical purposes (Duckworth et al., 1997; Brümmer and
Nickel, 2003).
The Mediterranean bath sponges of the genus Spongia are generally considered of high
commercial value for their characteristics, such as the fine texture of their fibres and
absorption properties (Verdenal and Verdenal, 1987). Moreover, the decline of natural
populations of the Mediterranean commercial sponges has led to their inclusion in the list
of organisms requiring specific management measures (Annex 3 of the Bern Convention
on the protection of Wildlife). Farming of these endangered species could thus contribute
to their conservation and restocking, as larvae produced by reared specimens can act as
new recruits able to re-colonise adjacent coastal areas (Manconi et al., 1998). Furthermore,
knowledge on growth patterns may contribute to designing restoration and conservation
plans. Indeed, experience in the cultivation of Spongia officinalis var. adriatica goes back
to the beginning of the past century (Cotte, 1908) and was more recently updated by
Verdenal and Vacelet (1990). Despite this, estimates of growth performance of reared
sponges are still sparse and not standardised, making the comparison between different
areas and cultivation techniques difficult.
The experiences of sponge culture reported in the literature so far are generally based
upon sponge cuttings sustained by suspended ropes and placed in the water column (e.g.
G. Corriero et al. / Aquaculture 238 (2004) 195–205
197
Verdenal and Vacelet, 1990) or laid close to the sea bottom (e.g. Grovas, 1998), depending
on the different cultivation environments (e.g. open sea or lagoons).
The main purpose of this work is to estimate the rearing performance of S. officinalis
var. adriatica, one of the most common Mediterranean commercial sponges, testing
structures differently placed along the water column, in order to simultaneously compare
the growth performance of reared sponges in relation to the two spatial orientations
reported above.
In addition, the resistance of the two differently oriented rearing structures to water
mechanical stress was also verified as well as the practical implications in terms of space
occupation and availability. Thus, sponges were suspended on ropes, horizontally near the
seabed and vertically along the water column. The trials were carried out in a coastal site
of the Apulia region (Gulf of Taranto, North Western Ionian Sea; Central Mediterranean).
2. Methods
The experiments were performed using S. officinalis var. adriatica, a species which is
black or deep grey in colour, lobed, highly variable in body shape and size and with small
conules and large oscules on the surface. The culture trials were performed from April
1997 to April 2000 in a nearshore site at 30-m depth, located along the coast of Apulia
(Porto Cesareo, Lecce; 40j15V.15 N –17j52V.50 E, 40j15V.16 N –17j52V.21 E; Fig. 1)
and characterised by a sandy seabed. The seed supply was collected by SCUBA divers
who only removed the upper portion of the sponge body, leaving a large fragment attached
to the substrate to allow regeneration. From hard bottoms adjacent to the cultivation site,
we collected 52 wild sponges that were each cut into explants of three sizes: 22.6 g
(n = 404; coefficient of variation: CV% = 21.7), 34.5 g (n = 256; CV% = 14.2), and 55.3 g
(n = 180; CV% = 16.6). A nylon rope was sewn through the sponge cuttings, which were
placed about 20 cm apart, operating onboard a boat in a 200-l plastic tank filled with
seawater and continuously renewed. Working under the sea surface, the nylon ropes were
then tied up to a plastic frame.
Two different types of rearing structures were prepared: in the former the plastic frames
were vertically assembled (vertical system) along the water column and anchored to the
bottom ( 30 m), with floaters on the upper end ( 18 m). The sponge cuttings were thus
placed between about 20 and 25 m. In the latter (horizontal system), the plastic
frames were positioned about 50 cm above the sea bottom (Fig. 2). In both the types of
rearing structures, the plastic frames were placed at a distance of about 50 cm from each
other.
About 70 small, 40 medium and 30 large explants were placed on three plastic frames
(Fig. 2), in three replicates positioned 3 m apart. A total of 202, 128 and 90 cuttings were
thus arranged in nine plastic frames per rearing system, which were situated 7 m from each
other.
According to a random sampling procedure, every 6 months, a sample of 30 reared
sponges from each cultivation system were cut from the ropes and collected using SCUBA.
Then, the main biometric parameters (wet weight and length expressed as major axes
diameter) were measured. The wet weight was assumed as a reliable and non-destructive
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Fig. 1. Porto Cesareo: map of the study area with location of culture site.
method for growth estimate, according to Duckworth et al. (1997). After measuring, the
sponges were re-utilised for restocking purposes in a different location and for a different
project.
The weight gain in two consecutive time intervals 6 months apart (final weight initial
weight) and the specific growth rate in weight were estimated, the latter as follows:
SGR ¼ ðloge Wt2 loge Wt1 Þ=ðt2 t1 Þ 100;
where loge are the natural logarithms, Wt2 and Wt1 the average wet weight at the two
different times, and (t2 t1) the time interval in days.
The occurrence of significant average-weight-at-time and growth (SGR) differences
between the two cultivation systems (vertical and horizontal) was evaluated by analysing
the three sizes of cuttings using the Friedman and post-Dunn tests (Siegel and Castellan,
1992), after having proved the non-homoscedasticity of the variances by the Cochran test.
A seasonal effect on growth was also tested, using the Mann –Whitney U-test.
The relationship between total wet weight at time t2, as a function of the same variable
at time t1 (t2 t1 = 6 months), as well as the regression between diameter and weight
(n = 84) were estimated on loge-transformed data (Draper and Smith, 1981), testing for the
significance of the square root of the coefficient of determination.
G. Corriero et al. / Aquaculture 238 (2004) 195–205
199
Fig. 2. (A) Scheme of the vertical (left) and horizontal (right) rearing structures. (B) Underwater image of the
vertical structure extended along the water-column. (C) S. officinalis var. adriatica cuttings sewn in nylon ropes.
(D) Specimens of S. officinalis var. adriatica after 3 years of culture.
The percentage survival rate (S) was estimated by considering the number of
individuals at the beginning of the experiment (N0) and the living specimens at the
successive steps of the rearing (Nt), correcting the values for the number of sampled
sponges:
S ¼ ðNt =N0 Þ 100:
Every third month, 10 sponges exclusively selected from the small cuttings were
sampled for the study of sexual reproduction. Samples of tissue were fixed in 4%
formaldehyde in seawater. Once in the laboratory, selected material was rinsed in seawater,
dehydrated and embedded in paraffin. The tissue analysis was carried out on histological
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sections 5 Am thick, stained with haematoxylin – eosin. For each fragment, five tissue
sections were observed under a microscope.
During the first year of the study (1997 – 1998), water temperature, salinity and
dissolved oxygen were measured monthly every 0.5-m depth, using a multi-parameter
probe (Idronaut Ocean Seven 501). Water movement was measured by a currentometer
(RCM9, Aanderaa Instruments, Norway) positioned at 26-m depth for 2 months (5856
measurements were collected).
3. Results
In the study area, the average monthly temperature of the water column (from the
surface to 30-m depth), the salinity and the dissolved oxygen showed the typical seasonal
pattern of Mediterranean temperate offshore waters. Temperature variations were from
11.9 (February) to 26jC (August) (Fig. 3). Generally, a homeothermic condition was
found in the water column, except during August –September when differences of about 4
jC occurred from the surface to the bottom. The salinity showed low fluctuations (range:
37.9– 38.4 ppt in November and March – April, respectively), while high oxygen concentrations were recorded, from 7.1 in September to 9.4 ppm in May (Fig. 3). In general, the
differences in the water column were not higher than 1 ppm.
The main current showed a preferential NW – SE direction and a sustained hydrodynamic circulation with a speed often from 10 –12 cm s 1 (range: 2 – 16 cm s 1).
The wave dynamics did not represent a limitation for either culture system because the
rearing structures were sufficiently elastic and placed under the wave breakdown zone (up
to 10 m from the surface).
In these environmental conditions, a better growth performance was generally recorded
from the vertical structures (Fig. 4). However, the average weight and the specific growth
Fig. 3. Seasonal variations of temperature, salinity and dissolved oxygen in the study area (the reported values
were averaged on the water column).
G. Corriero et al. / Aquaculture 238 (2004) 195–205
201
Fig. 4. Growth performance (mean weight in grams and specific growth rate in percentage) of S. officinalis
cuttings (small, medium and large) by cultivation system (hs = horizontal small; hm = horizontal medium;
hl = horizontal large; vs = vertical small; vm = vertical medium; vl = vertical large).
rate did not significantly vary (Friedman test: vF2(df = 5) = 1.91; p>0.05) between the
cultivation systems. In addition, no statistical difference in growth was detected between
the cuttings with different initial size.
The data were thus pooled (Fig. 5) and the following growth curve was estimated:
y = 35.441 e0.0015x (R2 = 0.97; Fig. 6), also using additional information available for the
4th year. The relationship between the weight at any two consecutive times was linear
according to the following equation: Wt2 = 0.9923 Wt1.068
.
1
The relationship between diameter (D) and wet weight (WW) was exponential,
describing an allometric growth in weight (WW = 1.4188 D2.06) with a significant
correlation coefficient ( p < 0.05). At the end of the rearing experiments, the harvested
sponges, despite the initial very irregular shape of the cuttings (Fig. 2C), were characterised by a rounded and regular profile (Fig. 2D), without the typical protuberances of the
wild specimens.
Fig. 5. Growth performance (specific growth rate in percentage) of S. officinalis cuttings: pooled data.
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Fig. 6. Growth curve and survival rate of S. officinalis.
The occurrence of a seasonal effect on specific growth rates was tested by comparing
the pooled time series of summer/autumn with that of winter/spring. The average spring
SGR (0.24) was higher than the autumn one (0.13) (Fig. 7), though no significant
difference was found ( p>0.05).
The survival rate, also including additional information available for the 4th year, was
75%, with a more apparent decrease during the first year (Fig. 6).
During the study period, embryos and larvae were found in the mesohyl of the sponge
cuttings in January 1998 (18.5% of the sample) for the first year; in October 1998 and
January 1999 (5.4% and 8.1% of the sample, respectively) for the second year, and in
April 1999 (15.1%) for the third year of study. Thus, relatively more intense reproductive
activity was registered during the cold season.
Fig. 7. Seasonal variations of growth (SGR) between pooled time series of S. officinalis cuttings.
G. Corriero et al. / Aquaculture 238 (2004) 195–205
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4. Discussion
The study was carried out in a coastal site well known for the richness of Porifera, and
particularly of the bath sponge S. officinalis var. adriatica (Pronzato et al., 1996; Corriero
et al., in press). This richness might be related to the high productivity of the Gulf of
Taranto, due to the inflow of nutrient-rich South Adriatic waters, especially during winter.
These environmental characteristics might have played a role in influencing the slightly
better growth performance, although not statistically significant, observed in spring during
this study. Seasonal growth differences, frequently reported for sponges (Stone, 1970;
Reiswig, 1973; Elvin, 1976; Johnson, 1979), may be related to different prey availability
affecting the food uptake of sponges, as observed for a Mediterranean population of
Dysidea avara (Ribes et al., 1999).
Sexual reproduction does not seem to have influenced growth performance. Reproductive explants occurred almost all year round, with the exception of summer, thus
confirming the prolonged sexual phase of this species (Scalera Liaci et al., 1971).
The sustained local current regime as measured during this study and the hydrodynamism of the area in general probably generate a rather homogeneous availability of
food in the water column, making the growth obtained in the horizontal and vertical
rearing structures comparable.
The statistical approach applied in the present study also showed similar growth
performance between the experiments, independently of the initial size of the explants.
This outcome is in contrast with previous experiences of sponge cultivation performed in
the Mediterranean (Moore, 1910), which reported that smaller explants of S. officinalis
grew more rapidly than larger ones. However, the initial experimental conditions
experienced by Buccich (Moore, 1910) could have been different and the analysis of
results is not strictly based on a formal quantitative approach.
The mean growth observed in this study was rather variable among sponge cuttings,
even considering the same rearing condition and size range. This may be due to the fact
that cuttings were obtained from specimens of presumably different age. According to the
literature, growth rates of sponges may be greater in younger than in older specimens
(Reiswig, 1973). In addition, Verdenal and Vacelet (1990) report a certain degree of
growth variability among cuttings of S. officinalis var. adriatica obtained from the same
specimen.
The commercial size of natural bath sponges commonly starts from about 10 cm in
diameter (Verdenal and Verdenal, 1987; Grovas, 1998). According to the diameter/weight
relationship reported above, such a size corresponds to about 200 g of wet weight, a
weight which cuttings of about 55 g reach in 3 years. Thus, this initial size seems the most
suitable for cultivation purposes as it reduces the rearing time. Smaller cuttings resulted in
lighter sponges (only about 100 g) after 3 years. However, the eventual choice of different
initial cutting sizes will depend on a trade-off between several factors, such as the
availability of seed, the rearing time up to the commercial size and the total amount of
planned production.
The final shape of the cuttings was mainly rounded, lacking the usual lobes and
irregularities, the latter caused by the adhesion to the substrate in natural specimens. In
addition, the skeleton of the sponges we got showed a more homogeneous texture and size
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(diameter) of the fibres, due to the scarcity of primary traits of spongin (Corriero et al.,
unpublished data). The growth, measured in this study as specific growth rate, assuming
an exponential growth pattern in the examined period, showed performances comparable
to the experiences of Verdenal and Vacelet (1990) for the Mediterranean. Conversely, the
growth rate of S. officinalis var. adriatica was slower than that reported for the Caribbean
species (Grovas, 1998).
The obtained survival rate showed a more critical phase during the first year, although
the mortality was generally lower in comparison to the data reported by Verdenal and
Vacelet (1990) for the Mediterranean S. officinalis. During this phase, two main factors
were acting on the recovery capability of the sponge cuttings, the first related to the
manipulation (collection, cutting, and sewing) and the second to the cicatrisation process
of tissue around the nylon ropes. Subsequently, additional but lower mortality occurred as
a result of competition with fouling organisms (i.e. Mytilus galloprovincialis, Ostrea
edulis, Sabella spallanzanii and colonial ascidians) whose larvae can settle near the
exposed skeletal tissue emerging from the area of the cutting subjected to abrasion by the
nylon rope. In contrast, the epibiontic frondose species of Hydrozoa and Bryozoa did not
seem to affect survival of cuttings.
Finally, both the horizontal and vertical systems proved to be resistant to deterioration
due to water movement as well as to other ecological factors. Indeed, the wave dynamics
do not represent a limitation if the rearing structures are placed under the wave breakdown
zone (up to 10-m depth from the surface). In the local conditions and during the
experienced time of rearing, fouling did not damage the submerged structures. Thus,
the choice of the most suitable system can mainly rely upon considerations related to space
availability and local hydrodynamic regime.
Acknowledgements
This research was supported by funds from the Italian Ministry of Agriculture and
Forest Policy.
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